There are a variety of known bottles and cans designed to contain pressurized materials. These include metal cans, such as those commonly used in conventional aerosol products, as well as plastic bottles, such as those commonly used for containing pressurized beverages. At least in laboratory settings, it is also known to use glass bottles to contain the sort of materials that, in the consumer market, are normally dispensed from metal cans.
It is also known to use plastic bottles with a dispensing valve for pressurized aerosol products. FIG. 1 shows an example of such a prior art bottle. It is unitarily formed and includes a plastic bottom 1, plastic side walls 2, and a plastic top 3 that is necked in to create a bottle mouth 4. An appropriate valve 5 (shown schematically in half-round) is then mounted in the bottle mouth.
The bottle mouth 4 has a radially extending rim 6, and such valves 5 have a downwardly extending skirt 7 that is crimped under the rim 6, as shown in FIG. 1. A sealing layer 8 is sometimes located on the top-most surface of the rim 6, sealing the valve 5 to the rim to retain pressure within the bottle. The sealing layer 8 can be either a resilient gasket or a layer of a sealant material.
The use of plastic containers for products has various advantages, including such things as allowing a user to see the contained product before purchase or to monitor product consumption and condition. However, such prior art plastic bottles have several shortcomings. Most are manufactured by a blow-molding process, in which a slug or pre-form of hot, soft plastic is inserted within a mold and then expanded with a compressed gas, such as air, to conform to the interior of the mold. A “slug” here refers simply to a mass of plastic.
A “pre-form” is typically a thick-walled plastic piece that may be formed by injection molding or other processes to have predictable dimensions. In blow molding, both slugs and pre-forms are heated and inserted within the mold before being expanded with compressed gas.
The result of blow molding can be a bottle of consistent external dimensions. Furthermore, it is even possible to so prepare the initial slug or pre-form that it includes successive layers of different plastics, resulting in a final bottle that has laminated walls. This is commonly done, for example, when an inexpensive plastic is used for the exterior layers of a bottle, forming the bulk of the bottle's structure. The exterior layers are co-formed with one or more internal, laminated layers of functionally different plastics.
The internal layers may be necessary because of their ability, for example, to seal in and retain pressurized gases that otherwise would migrate and escape through the plastic of the outer layer. Conventional plastic soft drink and catsup bottles are made with multiple layers to successfully contain those products.
However, the blow-molding process is inherently less precise in controlling wall thickness and features than are other techniques for molding plastics. This presents an increasing problem when it is desired to contain materials at increasing pressures. At some point, flaws or other weaker bottle locations will give way, causing bottle failure even though most of the bottle is still strong enough to contain the pressure.
In contrast to blow molding, the well known injection molding process can produce structures of very precise dimensional consistency. In injection molding, a mold is provided that defines all the surfaces of the object to be produced, including both exterior and interior surfaces. As a result, structure thickness and other features are not dependent on the vagaries of an initial slug of hot plastic, expanding under pressure. However, it is very difficult, and in many instances entirely impractical, to produce via injection molding a unitarily formed bottle with a necked-in top. There is no way to withdraw through the necked-in top the part of the mold that defines the bottle's larger internal shape.
As an alternative the art has proposed non-unitary manufacture of such bottles, creating first an open-bottomed, injection-molded bottle and then, secondarily, attaching a plastic bottom. See, for example, U.S. Pat. No. 5,346,659. (The disclosure of this patent and all other publications referred to herein are incorporated herein by reference as if fully set forth.) These means of manufacture require special equipment and also leave one or more plastic-to-plastic seams that can be points of inconsistent thickness or plastic crystal structure or other structural inconsistencies that can lead to an increased likelihood of failure under sufficiently challenging pressures.
By whatever technique they are formed, plastic bottles having cylindrical sides, a plastic bottom, and a necked-in plastic top tend to fail under pressure first at the necked-in top or the bottle bottom. Various strategies have been employed to counter this, including designing pressure-resisting shapes for bottoms and thickened walls in bottle tops or other means to strengthen plastic tops.
Some of the resulting bottle shapes require separate, additional bottom structures to allow, for example, a rounded bottle bottom to rest on a flat surface without tipping over. For an example of such a conventional structure, see in FIG. 1 the base cap 9. The ability to rest stably on a flat surface is important both in use and in handling the bottle in conventional filling lines and other manufacturing situations.
Even with these special shapes, however, bottle failure still can occur as a consequence of the limitations of blow molding or plastic-to-plastic seams, especially when less expensive and less strong plastics such as polyethylene terephthalate (commonly referred to as “PET”) are used to make the pressure-resisting structure and bulk of the bottle. While considerable bottle strength can be achieved even in conventional plastic bottles by use of more expensive, stronger plastics, such as polyethylene naphthalate (commonly referred to as “PEN”), the expense can be prohibitive if the bottle is intended for use with a product that cannot be sold competitively at a higher price.
Incidentally, commercial materials referred to in the art (e.g. and in this patent) as “PET”, “PEN”, or the like typically are primarily the plastic referred to, but may also include small amounts of other plastics added to adjust molding or other characteristics of the primary plastic. The nature of such minor additions is well understood in the art.
The art has also developed a number of containers made of a mix of materials to hold a variety of chemicals. See e.g. U.S. Pat. No. 4,561,555 (plastic side wall, metal top), U.S. Pat. No. 4,464,109 (plastic side wall, metallic cap), U.S. Pat. No. 2,686,081 (two different plastic sections), U.S. Pat. No. 2,476,446 (plastic side wall, metal collar), U.S. Pat. No. 2,753,088 (plastic side wall, metal end) and U.S. Pat. No. 3,685,684 (mixed plastic metal can). However, even these prior art approaches are not optimal when one tries to form the plastic main body in a blow molding process where inexpensive, preferably transparent, plastics are used.
It can therefore be seen that there is a need for an improved container for pressurized materials that combines the advantages of inexpensive and transparent plastic materials with the strength, reliability, and ease of handling of a conventional metal can.